According to your utility's water quality report (available at https://www.calwater.com/wq/ccr/2011...rtDistrict=las) your hardness is about 328.42ppm, or 19.2gpg. If you also know the amount of water your household uses, the experts here can tell you what size water softener you might need, as well as other conditioning which might be desirable. I'm no expert, but I would dump the 13-year-old Kenmore for something more modern. I think California has some requirements for softeners that you'll need to watch out for as well, but again, there are some experts here who know about things like that. If you're at all handy, you could probably install and maintain your own system. If not, find a local dealer you're comfortable with. As for in our out of the garage, that may be a local homeowners' beautification issue, but I don't think there's a technical reason, unless you're in a microclimate that has to contend with freeze events.
Here's a link to a basic softener sizing tool (http://www.qualitywaterassociates.co...izingchart.htm), but you're better off giving all your basic data (water quality and water use) to an expert who can take everything into account.